Technical Factsheet on: METHOXYCHLOR
List of Contaminants
As part of the Drinking Water and Health pages, this fact sheet is part of a larger publication:
National Primary Drinking Water Regulations
Drinking Water Standards
MCLG: 0.04 mg/L
MCL: 0.04 mg/L
HAL(child): 1 day: 0.05 mg/L; Longer-term: 0.05 mg/L
Health Effects Summary
Acute: EPA has found methoxychlor to potentially cause central
nervous system depression, diarrhea, and damage to liver, kidney
and heart tissue from short-term exposures at levels above the
MCL.
Drinking water levels which are considered "safe" for short-term
exposures: For a 10-kg (22 lb.) child consuming 1 liter of water
per day, upto a 7-year exposure to 0.05 mg/L.
Chronic: Methoxychlor has the potential to damage liver, kidney
and heart tissue and to retard growth from long-term exposure at
levels above the MCL.
Cancer: There is no evidence that methoxychlor has the potential
to cause cancer from lifetime exposures in drinking water.
Usage Patterns
Methoxychlor is preferred to DDT for use on animals, in animal
feed, and on DDT-sensitive crops such as squash, melons, etc.
Since methoxychlor is more unstable than DDT, it has less
residual effect. Compared to DDT, methoxychlor, is more toxic to
some insects & less toxic to others. It has been used extensively
in Canada for the control of biting flies, and is also effective
against mosquitoes and houseflies.
Available information indicates production of methoxychlor has
decreased: from 3.7 million lbs. in 1978 to 700,000 lbs in 1982.
In 1982 it was estimated that industries consumed methoxychlor as
follows: 43 percent as an insecticide for livestock and poultry,
29 percent on alfalfa crops and 29 percent on citrus.
Release Patterns
Release of methoxychlor to the environment occurs due to its use
as an insecticide for home and garden applications, livestock and
poultry, alfalfa, soya beans, forests (Dutch Elm disease) ,
ornamental shrubs, deciduous fruits and nuts, and vegetables
Other sources of release may include loss during the manufacture,
formulation, packaging, and disposal of methoxychlor.
From 1987 to 1993, according to EPA's Toxic Chemical Release
Inventory, methoxychlor releases to land and water totalled only
about 2000 lbs.
Environmental Fate
Methoxychlor does not tend to persist when released to soil or
water, and does not accumulate in fish.
If released to soil, methoxychlor is expected to remain
immobilized primarily in the upper layer of soil although a small
percentage may migrate to lower depths, possibly into groundwater
as suggested by the detection of methoxychlor in some groundwater
samples.
Measured soil sorption coefficient (Koc) values in various soil
are as follows: 9700 to 41,000 in sand, 80,000 to 86,000 in
coarse silt, 73,000 to 100,000 in medium silt, 80,000 to 100,000
in fine silt and 73,000 to 92,000 in clay. In another study, a
Koc of 620 was found in a water-sediment system.
This range of Koc values suggests that methoxychlor would be
moderately mobile to immobile in soil and adsorb significantly to
suspended solids and sediments in water. Methoxychlor was found
to migrate as much as 100 cm under conditions in which 95 to 97%
of the residues remained in the top 10 cm of soil.
Under anaerobic soil/sediment conditions, biodegradation appears
to be the dominant removal mechanism. In sediments, methoxychlor
was found to have a half-life of >100 days under relatively
aerobic conditions and < 28 days under anaerobic conditions.
Half-lives in anaerobic soils are about 3 months. Methoxychlor
may undergo indirect "sensitized" photolysis on the soil surfaces
and it may undergo chemical hydrolysis in moist soils (half-life
> 1 year).
If released to water, methoxychlor may be removed or transported
by several different mechanisms. Methoxychlor may adsorb to
suspended solids and sediments. It may undergo direct photolysis
(half-life 4.5 months) or indirect "sensitized" photolysis
(half-life <5 hours) depending upon the presence of
photosensitizers. Based on the Henry's law constant,
volatilization of methoxychlor may be significant (half-life 4.5
days from a shallow river).
Methoxychlor may also biodegrade in sediments, as mentioned
above, but oxidation and chemical hydrolysis are not expected to
be significant fate processes.
If released to the atmosphere, methoxychlor may exist in either
vapor or particulate form. Methoxychlor may undergo reaction with
photochemically generated hydroxyl radicals (estimated vapor
phase half-life 3.7 hours) or physical removal by settling out or
washing out in precipitation.
Significant bioconcentration has been measured in certain
shellfish, insects, algae and fish, although fish are generally
reported to metabolize methoxychlor fairly rapidly and do not
accumulate it.
The most probable route of exposure to methoxychlor would be
inhalation or dermal contact during home use of this insecticide,
inhalation of airborne particulate matter containing methoxychlor
or ingestion of food or drinking water contaminated with
methoxychlor.
Chemical/ Physical Properties
CAS Number: 72-43-5
Color/ Form/Odor: Colorless crystals with slightly fruity odor;
available as: wettable powder; emulsifiable, dust and aerosol
concentrates; oil solutions
M.P.: 89 C B.P.: N/A
Vapor Pressure: very low
Density/Spec. Grav.: 1.41 at 25 C
Octanol/Water Partition (Kow): Log Kow = 4.83, 4.91 and 5.08
Solubility: 0.10 mg/L of water at 25 C; Slightly soluble in
water
Henry's Law Coefficient: 1.6x10-5 atm-cu m/mole at 25 C
Odor/Taste Thresholds: odor threshold is 4.7 mg/L in water
Soil sorption coefficient: measured Koc ranges from 9700 to
41,000 in sand to 80,000 to 100,000 in fine silt; low mobility in
soil
Bioconcentration Factor: BCFs of 1500 to 8500 in shellfish and
algae, much lower in fish; expected to bioconcentrate in aquatic
organisms.
Trade Names/Synonyms:
2,2-bis(p-methoxyphenyl)-1,1,1-trichloroethane, dianisyl
trichloroethane, Dimethoxy-DDT, Methoxy-DDT, Chemform, Maralate,
Methoxo, Methoxcide, Metox, Moxie
Other Regulatory Information
Monitoring For Ground/Surface Water Sources:
- Initial Frequency- 4 quarterly samples every 3 years
- Repeat Frequency- If no detections during initial round:
- 2 quarterly per year if serving >3300 persons;
- 1 sample per 3 years for smaller systems
- Triggers - Return to Initial Freq. if detect at > 0.0001 mg/L
Analysis:
| Reference Source |
Method Numbers |
| EPA 600/4-88-039 |
505; 508; 508.1; 525.2 |
Treatment- Best Available Technologies:
Granular Activated Charcoal
For Additional Information:
EPA can provide further regulatory and other general information:
EPA Safe Drinking Water Hotline - 800/426-4791
Other sources of toxicological and environmental fate data include:
Toxic Substance Control Act Information Line - 202/554-1404
Toxics Release Inventory, National Library of Medicine - 301/496-6531
Agency for Toxic Substances and Disease Registry - 404/639-6000
National Pesticide Hotline - 800/858-7378
List of Contaminants
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